From the Guidelines
The initial workup for suspected insulinoma involves confirming hypoglycemia with Whipple's triad, followed by laboratory tests during a hypoglycemic episode, including serum insulin, C-peptide, and proinsulin levels, which will be inappropriately elevated in insulinoma, as supported by 1 and 1.
Initial Workup
The diagnosis of insulinoma is based on the following criteria:
- Symptoms of hypoglycemia
- Documented low blood glucose <50 mg/dL
- Resolution of symptoms with glucose administration A 72-hour supervised fast is the gold standard diagnostic test, during which blood samples are collected when the patient becomes symptomatic or glucose falls below 45 mg/dL, as recommended by 1 and 1.
Localization Studies
Once biochemical diagnosis is established, localization studies including:
- Contrast-enhanced CT
- MRI
- Endoscopic ultrasound
- Sometimes selective arterial calcium stimulation testing, as suggested by 1 and 1 should be performed to identify the tumor.
Initial Treatment
Initial treatment focuses on preventing hypoglycemia through:
- Frequent small meals high in complex carbohydrates
- Avoiding simple sugars
- Diazoxide (starting at 150-200 mg/day in divided doses, maximum 600 mg/day) can be used to inhibit insulin release, as recommended by 1 and 1
- Octreotide (100-500 mcg subcutaneously 2-3 times daily) may help in some cases, but should be used with caution in patients with insulinoma, as noted by 1 and 1
- Glucocorticoids and glucagon are reserved for emergency management of severe hypoglycemia.
Definitive Treatment
Definitive treatment is surgical resection of the tumor, which is curative in most cases, as stated by 1 and 1. For patients who are not surgical candidates or have metastatic disease, continuous medical therapy with diazoxide or everolimus may be necessary for long-term management, as suggested by 1 and 1.
From the Research
Initial Workup for Suspected Insulinoma
- The initial workup for a suspected insulinoma typically involves a supervised fast with serial measurements of plasma glucose, insulin, and C-peptide 2, 3.
- The supervised fast can be performed for 48 hours or 72 hours, with the 48-hour fast being considered a sufficient diagnostic standard in some cases 3.
- During the fast, patients are monitored for symptoms of hypoglycemia, and blood samples are taken at regular intervals to measure glucose, insulin, and C-peptide levels.
- Proinsulin levels can also be measured, as even mild elevations in circulating proinsulin can be an independent indicator of aberrant insulin secretion during hypoglycemia 2.
Diagnostic Criteria
- The diagnosis of insulinoma is based on demonstrating Whipple's triad during a supervised fast, which includes:
- Symptoms of hypoglycemia
- Low plasma glucose concentration
- Inappropriately high insulin and C-peptide levels during hypoglycemia 3
- Immunoreactive proinsulin can be elevated at the beginning of the fast in patients with insulinoma, and samples taken in the suppressed state have the greatest diagnostic value 3.
Tumor Localization and Treatment
- Once the diagnosis of insulinoma is made, tumor localization can be achieved using imaging studies such as spiral CT, magnetic resonance imaging, and endoscopic ultrasound 2.
- Minimally invasive tumor resection is a safe and effective treatment modality for insulinoma, and can be performed without complications in many cases 2.
- Preoperative treatment with diazoxide or somatostatin analogues may be required to prevent severe hypoglycemia, especially in cases where surgery is contraindicated, delayed, or refused 4.
- A stepwise algorithm for the management of hypoglycemia can be proposed, stratified by localized versus metastatic disease, and including nutritional management, pharmacological management, and other therapeutic interventions 5.